1. Technical Field
The present disclosure relates to a display device and a drive method for the same. The present disclosure also relates to an electronic apparatus with the display device.
2. Description of the Related Art
Recently, there is a growing need for display devices optimized for, for example, mobile devices such as mobile phones and electronic papers. The display device is configured that one pixel has a plurality of sub-pixels, each of which emits light in a different color, and a display of the sub-pixel is turned on or off, to thereby display various colors using one pixel. Some of the display devices include those in which four sub-pixels including white are made to one pixel (see Japanese Patent Application Laid-open Publication No. 2010-33009 (JP-A-2010-33009) and Japanese Patent Application Laid-open Publication No. 2011-248352 (JP-A-2011-248352)).
JP-A-2010-33009 describes a display device that includes an image display panel on which pixels each including first, second, third, and fourth sub-pixels are arranged in a two-dimensional matrix and a signal processing unit that receives an input signal and outputs an output signal. The display device can enlarge an HSV (Hue, Saturation, Value) color space more than three primary colors by adding a fourth color to the three primary colors. The signal processing unit stores therein a maximum value Vmax(S) of a value (brightness) based on a saturation S functioning as a variable, calculates the saturation S and the brightness V(S) based on the signal value of the input signal, calculates an extension coefficient α0 based on at least one of values of Vmax(S)/V(S), calculates an output signal value for the fourth sub-pixel based on at least input signal values for the first, the second, and the third sub-pixels, and calculates output signal values for the first, the second, and the third sub-pixels based on the input signal values, the extension coefficient α0, and the output signal value for the fourth sub-pixel.
JP-A-2011-248352 describes a display device that includes a display panel on which a plurality of pixels each having sub-pixels with red, green, and blue color filters and a sub-pixel for controlling transmission of white light are provided; a backlight unit including red, green, blue, and white light sources; an image switching circuit for switching whether to display the display panel in a moving image mode or in a still image mode; and a display control circuit that controls respective luminance of red, green, and blue in the backlight unit according to an image signal in the moving image mode and controls luminance of a white light source in the backlight unit according to an image signal in the still image mode. Japanese Patent Application Laid-open Publication No. 2011-154323 (JP-A-2011-154323) describes a display device in which a signal processing unit calculates a saturation S and a brightness V(S) of a plurality of pixels based on input signal values of sub-pixels in the plurality of pixels, and determines an extension coefficient α0 so that a proportion of pixels, each of which a value of the extended brightness calculated from a product of the brightness V(S) and the extension coefficient α0 exceeds the maximum value Vmax(S), to all the pixels becomes a predetermined value (β0) or less.
As described in JP-A-2010-33009, JP-A-2011-248352, and JP-A-2011-154323, an image signal is extended corresponding to an HSV area enlarged by using one sub-pixel (basically, a white sub-pixel) among the sub-pixels based on the image signals to thereby decrease the light amount of the light source, thus reproducing a desired image. Moreover, an image can be made bright without increasing the light amount of the light source.
However, there may be a case in which extension of the image signal causes the image quality to lower (degrade). On the other hand, there may be a case in which the display device described in JP-A-2011-154323 is used to determine the extension coefficient and this thereby enables to suppress degradation of the image quality but reduction of power consumption becomes less effective.